<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      ul {
        display: none;
      }
      .menu:hover a {
        color: yellow;
      }
      .menu:hover ul {
        display: block;
      }
    </style>
  </head>
  <body>
    <section class="menu">
      <a href="#">演示hover效果</a>
      <ul>
        <li>123</li>
        <li>456</li>
      </ul>
    </section>
  </body>
</html>
